Description:
------------
double free on recursively call to list dtor

Test script:
---------------
<?php

class O {
    public $ch;
    public function dummy() {
    }
}

$ch = curl_init();

$o = new O;
$o->ch = $ch;
curl_setopt($ch, CURLOPT_WRITEFUNCTION, array($o, "dummy"));

Expected result:
----------------
non segfault

Actual result:
--------------
segfault